Environmental stress shapes plant development in part by affecting transcription factor (TF) networks. Comprehending these networks and how they respond to external stimuli is key to understanding both animal and plant development. Our long-term goals are 1) to understand how environmental signals are perceived and translated into developmental changes in the plant root, 2) to develop a profile of the root transcription network under various environmental stresses, and 3) to use this information in generating a systems biology approach towards understanding plant development and to look for broad commonalities between plant and animal transcription networks. We will focus on aluminum (Al) toxicity to study the relationship between environmental stress, root development, and transcription networks. Toxic levels of Al inhibit growth of the primary root, and are often found in acidic soils. Since TFs are essential to plant developmental processes, which are in turn affected by the environment, their expression should change in response to external stress. Thus, we hypothesize that Al inhibits root elongation by affecting the expression and/or protein localization of transcription factors involved in cell proliferation and elongation, two of the major processes in organ growth. Our lab has developed a protocol based on sorting fluorescently marked cell types to examine global gene expression at cell-specific resolution, and used it to develop an Arabidopsis root expression map under unstressed conditions. We will apply this method to understand TF responses to Al stress, and how such responses result in the inhibition of organ growth and development in Arabidopsis. Our specific aims are to: 1. Identify morphological changes in 6 different root cell types in response to Al with fluorescently marked cell lines. Although whole root effects of Al have been studied, effects of Al on specific root cell types are not well known. 2. Identify the set of genes affected by Al stress in the whole Arabidopsis root with microarray analysis. To identify potential tissue types most strongly affected by the stress, we will cross reference genes identified here with our root expression map created under unstressed conditions. 3. Perform detailed cell-specific microarray analysis on tissue types most affected by Al and identify the most altered TFs. 4. Clarify the role of selected TFs in Al toxicity and root growth by mutant characterization. 5. Examine selected TF expression in Arabidopsis accessions with different sensitivities to Al. Though plant and animal developmental processes are clearly different, the same basic problems had to be solved to result in a successful multicellular organism. The complex interactions through which life develops are thus likely to follow broadly parallel patterns.